The present invention is related to an apparatus and method for communicating optical signals to an electronic device enclosed within a flip-chip package.
Commonly available electronic devices exist in the form of a thin sheet of semiconductor material, or die, with electronic circuitry disposed thereon by way of various photolithographic processes. To protect the circuitry from damage, the die is often enclosed in a package designed to facilitate the attachment of the electronic device to a printed circuit board of a computer system or other electronic system.
Within some electronic devices are components meant to produce optical signals to be transmitted outside of the package, or to receive optical signals to be received from outside of the package. Packages have been used that provide a window through which such signals may pass. The window of such packages typically faces outwardly from the package in a direction that is generally meant to face away from the printed circuit board to which the electronic device is to be attached. One of the most common examples of such electronic devices enclosed within such a package is an ultaviolet-eraseable programmable read-only memory or UV-EPROM.
FIG. 1 is a cross-sectional view of a prior art package of the dual inline pin (DIP) type. The exterior or package 100 is comprised of window 110 and shell 112. Die attach 114 attaches die 130 to an inner surface of shell 112, thereby securing die 130 to the interior of package 100. Bonding wires 120 provide part of the electrical connections between die 130 and solder balls 122. Die 130 is positioned within package 100 such that the surface on which electronic circuitry (not shown) has been disposed is caused to face window 110 to allow the transmission or receipt of optical signal 132. Pins 122 are used to attach package 100 to printed circuit board 140 through which are holes to receive the pins, and as a result, window 110 faces away from printed circuit board 140.
The use of such packages, however, is based on a long-standing practice of having the surface of the die on which electronic circuitry is disposed facing away from the printed circuit board to which the electronic device is attached, thereby making this surface of the die accessible to optical signals passing through the window of the package. More recently, however, flexibility in power consumption and die size, as well as improvements in electrical signal characteristics, have been realized through the use of packages, such as the xe2x80x9cflip-chipxe2x80x9d or the xe2x80x9ccontrolled collapsed chip connectionxe2x80x9d (C4) package, in which the surface of the die on which electronic circuitry is disposed now faces towards the printed circuit board to which the electronic device is to be attached.